Our objective is to attempt to isolate, identify, and characterize the non- androgenic testicular substance(s) that stimulates prostatic growth. Two known etiological factors for the development of benign prostatic hyperplasia (BPH) in man is aging and the presence of functional testis. Yet, BPH develops at an age when serum levels of androgen are declining in an accessory sex gland whose function, growth, and structural maintenance are normally androgen-dependent. Consequently, with regard to available androgen, BPH development constitutes a paradoxical growth. Results of our earlier studies demonstrate that the testis is able to stimulate prostatic growth aside from its ability to secrete androgen. If, as we postulate, this non-androgenic accessory sex gland stimulating testicular factor is associated with tubular secretory activity, it has the potential to have both a local as well as systemic effect on the human prostate because of the anatomical relationship of the ejaculatory orifices to the prostatic urethra. We postulate that BPH in man is a consequence of the local and/or systemic effect on the prostate resulting from changes in testicular tubular secretory activity that is initiated in response to aging and secondarily results in stimulation of prostatic growth in the presence of androgen. Two approaches are proposed. The in vivo approach will use animal models in an attempt to elucidate the systemic effect of the non- androgenic factor in the testis. Circulating levels of known testis- associated proteins will be measured, such as androgen-binding protein and inhibin, in addition to testosterone. Prostatic response to this testicular factor will be further characterized in order to develop a cellular marker to this systemic testicular non-androgenic factor. The in vitro approach will use cultures of epithelial and stromal cells from human and animal prostates in an attempt to identify the local factor which is present in the seminal plasma and spermatocele fluid. Our existing protocol calls for the use of analytical tools to fractionate these body fluids until the active fraction contains a single protein spot in the two- dimensional electrophoresis profile. Subsequent study will include characterization of the purified substance, development of polyclonal antibody, and immunohistochemical localization studies of the testis and the prostate to further elucidate its action.